Manufacture of alternating current rectifiers of the dry surface contact type



' Patented Aug. 13', 1940 MANUFACTURED! ALTERNATING CURRENT V RECTIFIERSOF THE DRY SURFACE CON- Albert Leslie Williams and Leslie ErnestThompson, London, England, assignors, by mesne assignments, to The UnionSwitch & Signal Company, Swissvale, Pa a corporation of Pennsyl vania NoDrawing. Application April 26, 1939, Serial No. 270,200. In GreatBritain May 14, 1938 11 Claims.

This invention relates to the manufacture of alternating currentrectifiers of the dry surface contact type, comprising a body of metalhaving an oxide of the metal'formed directly thereon by subjecting thebody to the action of an oxidising atmosphere, and has for its object toimprove the process of oxidisation'where'by certain important advantagesare obtained.

An important desirable quality in an oxide N rectifier is that itselectrical resistance in the w amongst other'conditions, upon the amountof reverse direction of current flow should be stable and not liable toappreciable creep or continuous change when voltage is applied, andexperience indicates that this creep is dependent free oxygen occludedin the oxide film or layer after its formation.

According to the present invention a substance capable of reducing theamount of free oxygen occluded in the oxide layer during its formationis arranged to be introduced into the oxidising;

' atmosphere employed. In particular, in the case of copper oxiderectifiers comprising a copper body or blank provided with a coating orlayer of cuprous oxide formed directly thereon by heating the blank to asuitable temperature in an oxidising atmosphere, advantageous resultsare obtained by introduction of a small quantity of the element boroneither 'in the combined or uncomblned state into the oxidising furnaceduring the heat treatment of the copperblanks.

In carrying the invention into practice, the boron either uncombined orcombined in the form of boric acid or borax for example, may beintroduced into the oxidising atmosphere in var= ious ways. The boron orboron compound may for instance be injected into the oxidising funnacechamber in the form of vapour or a cloud of finely divided particles.Alternatively, a suit- 40 able receptacle or reservoir containing theboron or boron compound may be located within the furnace chamber, orthe copper blanks, or their supports or carriers may be immersed in asuitable solution of a boron compound prior to the oxidising process.

In order to ensure the uniform distribution of the added substance thefurnace chamber employed is preferably provided with a non-, porouslining and with arrangements for effecting a circulation or agitation ofthe oxidising atmosphere within the chamber, for example, by

means of an injected stream of air-or oxygen.

The addition of boron to the oxidising atmosphere in the case of copperoxide rectifier-s, is

g found to eifect a considerable reduction in the initial reversecurrent and the reverse creep at all impressed voltage while theuniformity and crystalline structure of the cuprous oxide formed is muchimproved. 1

Furthermore, the undesired formation of cupric oxide is reduced, only anextremely thin superficial layer of this compound being formed.

Although the initial forward resistance of the rectifier element isincreased by the use of boron to an extent dependent upon the amount ofthis substance employed, this disadvantage can be offset by reducing thethickness of the cuprous oxide film which is permissible owing to itssuperior quality and to the small amount of cupric oxide formed asaboveexplained.

The amount of boron utilised will evidently depend upon particularconditions, but is in any case extremely small relative to the amount ofoxygen in the oxidising atmosphere.

It will be understood that similar advantageous results may probably beobtained by the addition of substances other than boron which hashowever been definitely determined to be particularly suitable in thecase of copper oxide rectiflers. The invention is however not limited inthis and other respects to the particular processes and arrangementsabove described is way of example.

Having now particularly described and ascer= tained the nature of oursaid invention and in what manner the same is to be performed, wedeclare that what we claim is:

1. The process for manufacturing a copper oxide rectifier whiohcomprisessubjecting a copperbody to the action of an oxidizing atmosphere intowhich the element boron in a combined or an uncombined state has beenintroduced to reduce the amount of free oxygen occluded in the oxidelayer during its formation.

2. The process for manufacturing a copper oxide rectifier whichcomprises subjecting a copper body to the action of an oxidizingatmosphere into which boron or a boron compound has been introduced inthe form of a vapor or cloud to reduce the amount of free oxygenoccluded in the oxide layer during its formation.

3. The process for manufacturing a copper oxide rectifier whichcomprises heating a copper body in an oxidizing atmosphere in a furnacehaving located in the oxidizing chamber a receptacle containing boron'ora boron compound.

4. The process for manufacturing a copper oxide rectifier which consistsin. subjecting a copper bodytothe action of an oxidizing at mospherewhile mounted on a support or carrier which has previously been immersedin a solution of a boron compound.

5. The process for manufacturing a copper oxide rectifier which consistsin subjecting a copper body to the action of an oxidizing atmosphereinto which borax or boric acid has been introduced.

6. The process for manufacturing a copper oxide rectifier which consistsin heating a copper body in a furnace in an oxidizing atmosphere intowhich boron or a boron compound has been introduced, the oxidizingatmosphere being circulated or agitated by means of an injected streamof air or oxygen.

7. The process for manufacturing a copper oxide rectifier which consistsin subjecting a copper body to the action of an oxidizing atmosphere,into which boron or a boron compound has been introduced to effect areduction in the initial reverse current at all impressed voltages.

8. The process for manufacturing a copper oxide rectifier which consistsin subjecting a copper body to the action of an oxidizing atmosphereinto which boron or a boron compound has been introduced to effect areduction in the reverse creep at all impressed voltages.

9. The process for manufacturing a copper oxide rectifier which consistsin subjecting a copper body to the action of an oxidizing atmosphereinto which boron or a boron compound has been introduced to improve theuniformity and crystalline structure of the cuprous oxide which isformed.

10. The process for manufacturing a copper oxide rectifier whichconsists in subjecting a copper body to the action of an oxidizingatmosphere into which boron or a boron compound has been introduced toreduce the formation of cupric oxide.

11. The process for manufacturing a copper oxide rectifier whichconsists in subjecting a copper blank to the action of an oxidizingatmosphere into which has been introduced boron in an amount which isextremely small relative to the amount of oxygen in the oxidizingatmosphere.

ALBERT LESLIE WILLIAMS.

LESLIE ERNEST THOMPSON.

